The present invention relates to the field of implantable medical devices. More particularly, the present invention relates to systems and methods for monitoring septums in implantable medical devices.
Many implantable medical devices require percutaneous communication with devices external to the body in which the implantable medical device is located. For example, implantable medical devices that dispense drugs within the body may require periodic replenishment of the drug located in a reservoir of the device. Typically, such replenishment is accomplished by advancing a needle (or similar device) through the skin into a reservoir of the device and transferring fluids through the needle.
Because the device is implanted within the patient and cannot be seen directly, care must be taken to ensure that the needle is properly placed into the device before transferring fluids. If the needle is not located within the reservoir, delivery of the drug through the needle can result in immediate delivery of a significant quantity of the drug to the patient, with potentially dire consequences. In addition, failure to properly refill the reservoir may also have potentially dire consequences for the patient when the needed medication is not dispensed at a later time.
Attempts to address the problem of needle location within a septum have taken two general approaches. In one set of approaches, the location of the septum is determined by various techniques including antennas located on the surface of the patient. One potential issue with this approach is that even after location of the septum is accurately determined, perforation of the septum by the needle may not necessarily be guaranteed during fluid transfer.
Another set of approaches involves determining whether the needle is located within the reservoir after it has been advanced. One variation of this approach involves closing an electronic circuit to provide an indication that the needle is in physical contact with a selected location within the reservoir. Another variation involves providing tactile and/or audible feedback to the operator of the needle when the needle causes deflection of a resilient portion of the reservoir. Another approach to determine whether a needle has pierced a septum in an implantable medical device involves sensing the location of needle within the reservoir by detecting a change in impedance of an air inductor or an eddy current detector within the reservoir of the device.
Still another approach involves the use of a multi-layered septum including conductive layers. When a needle pierces the septum, electrical connection between the conductive layers through the needle piercing the layers provides an indication that the septum has been pierced. One issue with this approach is that one of the conductive layers may need to be exposed within the reservoir, which may not be desirable if the conductive materials are not compatible with the drugs or other materials located within the reservoir.
Another issue with many of these approaches is that the needle itself must be electrically conductive. As a result, more recent advancements in the use of polymeric needles may be incompatible with many of these approaches because polymeric needles will typically be electrically nonconductive.
Examples of these approaches may be described in one or more of the patents listed in the following Table I.
All references listed in Table I, and elsewhere herein, are incorporated by reference in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments, and claims set forth below, at least some of the devices and methods disclosed in the references of Table I and elsewhere herein may be modified advantageously by using the teachings of the present invention. However, the listing of any such references in Table I, or elsewhere herein, is by no means an indication that such references are prior art to the present invention.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to septums located in implantable medical devices. One such problem is that, in some situations, it is difficult or impossible to determine whether a needle meant to pierce a septum is, in fact, present in the septum. As a result, drugs may not be properly delivered to the reservoirs of implantable medical devices through septums in those devices. As noted above, in some situations the drug may be dispensed directly to the patient with potentially dire consequences. In other situations, the drug is not available in the reservoir of the implantable medical device for dispensing when needed at a later time.
In comparison, the systems and methods of the present invention can be used to monitor the condition of a septum in an implantable medical device. Monitoring of the septum provides the ability to determine whether a needle has pierced the septum to effect the transfer of fluids into or out of a reservoir in the implantable medical device. Alternatively, monitoring of the septum may provide the ability to determine whether the septum is maintaining its ability to seal the reservoir against leakage.
The systems of the present invention include an ultrasonic transducer mounted to direct ultrasonic energy into the septum. The ultrasonic transducer is preferably directly acoustically coupled to the septum. Insertion of a needle into the septum can be detected by the acoustical changes caused by the needle located within the septum. The ultrasonic transducer can be operated in either pulse mode or impedance mode. In pulse mode, a short electrical pulse is used to drive the ultrasonic transducer. The ultrasonic transducer converts the electrical energy into acoustic energy traveling through the septum.
In the absence of a needle, the ultrasonic energy will typically be reflected by the opposing side of the opening in which the septum is located. Insertion of a needle into the septum will, however, result in an early reflection of the ultrasonic energy directly from the needle, and/or a change in the pattern of reflected ultrasonic energy within the opening. Such changes in reflection of the ultrasonic energy can be used to provide an indication that the septum has been pierced by a needle.
If the ultrasonic transducer is operated in impedance mode, the transducer is driven (by, for example, a swept sine wave) while measuring its response. The response of the ultrasonic transducer is indicative of the acoustic load on the ultrasonic transducer for each applied frequency. That acoustic load will be changed by the insertion of a needle into the septum, degradation of the septum, leakage around the septum, etc.
Whether the ultrasonic transducer is driven in pulse mode or impedance mode, it may be desirable to compare measurements obtained at different times to determine whether a needle is present within the septum. Typically, such comparisons will be made based on a reference signal identified shortly before advancement of the needle, followed by signals obtained after advancement of the needle by an operator.
The decision to obtain a reference signal can be invoked by telemetric communication with the implantable medical device to provide an indication that a transfer procedure is about to occur. At that point, a reference signal can be obtained using the ultrasonic transducer before the needle is inserted through the skin of the patient. From that point in time, repeated measurement cycles may be performed until detection of the needle piercing the septum occurs.
Another advantage of the systems and methods of the present invention is their compatibility with polymeric needles that are typically electrically nonconductive. Many of the previous approaches to sensing needle presence in a septum have relied on electrically conductive needles that are typically metallic. The systems and methods of the present invention are, however, capable of detecting any needle that presents a hard, acoustically reflective surface, regardless of the electrical conductivity of the material or materials used to construct the needle.
An additional advantage of the present invention is that further measurements with the ultrasonic transducer may be obtained after removal of the needle from the septum. Such measurements may be used to provide an indication regarding the condition of the septum after removal of the needle. One use for such a measurement is to determine whether the condition of the septum is such that leakage may be occurring through or around the septum.
These and other objects, advantages, and features of the invention may be understood more completely with reference to the following detailed description of specific embodiments of the invention.